1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system having the sheet processing apparatus.
2. Description of the Related Art
An image forming system includes an image forming section for forming an image on a sheet and a sheet processing apparatus for performing various processing on the sheet on which the image is formed. The “various processing” performed by the sheet processing apparatus include, for example, a center folding processing, a trimming processing, a square back processing and the like, wherein the center folding processing is adapted to center-fold the sheet, the trimming processing is adapted to trim the end portion of a sheet bundle formed by a plurality of folded sheets, and the square back processing is adapted to transform the folded end portion of the sheet bundle into a square-shaped back surface.
Conventionally, when conveying the center-folded sheet bundle to a processing section where the trimming processing and the square back processing are performed, the sheet bundle is sandwiched so that the sheets are not out of alignment. Such conventional sheet processing apparatus is described in, for example, Japanese Unexamined Patent Application Publication No. H09-278275 (referred to as “Patent document 1” hereinafter). Patent document 1 proposes an art in which a pair of rollers are provided, and a sheet bundle is conveyed while an end portion of the sheet bundle is sandwiched by the pair of rollers.
Further, Japanese Unexamined Patent Application Publication No. 2011-25369 (referred to as “Patent document 2” hereinafter) proposes an art which includes a placing table on which a sheet bundle is placed, and a table moving mechanism for moving the placing table substantially in the horizontal direction. According to the art described in Patent document 2, the sheet bundle is placed on the placing table in a state where the planar portion of the sheets faces the placing table, and the placing table is moved substantially in the horizontal direction in a state where the sheet bundle is placed on the placing table, so that the sheet bundle is conveyed to a processing section which performs the trimming processing. Further, an end portion of the sheet bundle to be subjected to the trimming processing is sandwiched before performing the trimming processing.
A position control mechanism for controlling the position of the sheet bundle is described in, for example, Japanese Unexamined Patent Application Publication No. 2009-202553 (referred to as “Patent document 3” hereinafter). A post-processing device described in Patent document 3 conveys the center-folded sheet bundle in the horizontal direction in a manner in which the fold of the sheet bundle faces forward. Further, a protrusion amount regulating member abuts the outer side of the fold of the sheet bundle so as to regulate the position of the sheet bundle, and the square back processing is performed so that the folded end portion of the sheet bundle is transformed into a square-shaped back surface.